Implantable drug delivery systems and methods

ABSTRACT

Devices, systems and methods for delivering one or more drugs to one or more internal body locations (such as the cerebrospinal fluid) are disclosed. In various aspects, the systems and methods may involve catheters having infusion sections with permeable membranes that develop significant back pressure to enhance uniform delivery of the drug over an infusion section; catheters that have two or more infusion sections spaced apart along the length of the same catheter, catheters that include two or more infusion sections serviced by independent lumens (such that, e.g., different drug solutions can be delivered to the different infusion sections); implantable drug delivery systems with pumps and multiple reservoirs from which drugs can be delivered; systems that are capable of delivering drug solutions with selected densities; etc.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. Section119(e) of U.S. Provisional Application No. 60/436,294 titled CATHETERSAND METHODS FOR THERAPEUTIC SUBSTANCE DELIVERY, filed on Dec. 23, 2002and U.S. Provisional Application No. 60/508,353 titled CATHETERS ANDMETHODS FOR THERAPEUTIC SUBSTANCE DELIVERY, filed on Oct. 3, 2003, bothof which are hereby incorporated by reference in their respectiveentireties.

BACKGROUND

There are a number of conventional devices available for deliveringdrugs to a patient. More specifically, completely implantable drugdelivery systems are available. Examples include the ISOMED andSYNCHROMED implantable pumps available from Medtronic, Inc.,Minneapolis, Minn. USA.

Completely implantable drug delivery systems typically include a pumpwhich stores and infuses the drug in a desired infusion mode and rate,and a catheter which routes the drug from the infusion pump to thedesired anatomic site. Implantable pumps may be large and are typicallyimplanted in areas of the body with available volume that is notcompletely filled with body organs, such as the abdomen. The target sitefor drug infusion may, however, be located at a distance from the pump.A thin flexible catheter is typically implanted to provide a guidedpathway for drugs from the pump to the target location.

Implantable pumps are often used to treat neurological diseases;examples are chronic pain and intractable spasticity. These conditionsrequire treatment for a long time, frequently for the lifetime of thepatient. An implantable pump can deliver drugs at a desired rate withoutintervention for a long time, and make drug therapy much easier and moreaccurate. Large doses of oral drugs would be required since theblood-brain barrier prevents most of the drug from reaching the centralnervous system. Some of the drug that is blocked by the blood-brainbarrier will instead travel to other organs, and can cause undesirableside effects. A catheter can, however, penetrate the membranes thatcomprise the blood-brain barrier and infuse the drug directly to thetarget receptors.

The neurological drug receptors for many therapies, such as pain andspasticity, are located in the spinal cord. A catheter cannot besurgically connected to the spinal cord because it could damage otherneurons and cause serious neurological problems. The brain and spinalcord are surrounded by cerebrospinal fluid (CSF). CSF provides acushioning effect for the spinal cord, but also provides a vehicle todeliver substances such as proteins, glucose, and ions (e.g. sodium,calcium, and potassium) to the central nervous system. Neurological druginfusion systems are designed to utilize this property of CSF. The drugis infused into CSF and then distributed through the CSF to thereceptors in the spinal cord. These systems typically rely on infusionat one location.

Other limitations of known implantable systems and methods of drugdelivery is that the systems may be limited to a single reservoir fromwhich only one drug solution can be delivered at any given time. Thedensity of the drug solutions delivered by such systems cannot bechanged after implantation of the devices.

SUMMARY OF THE INVENTION

The present invention provides systems and methods for delivering one ormore drugs to one or more internal body locations (such as the CSF). Invarious aspects, the systems and methods may involve catheters havinginfusion sections with permeable membranes that develop significant backpressure to enhance uniform delivery of the drug over an infusionsection; catheters that have two or more infusion sections spaced apartalong the length of the same catheter, catheters that include two ormore infusion sections serviced by independent lumens (such that, e.g.,different drug solutions can be delivered to the different infusionsections); implantable drug delivery systems with pumps and multiplereservoirs from which drugs can be delivered; systems that are capableof delivering drug solutions with selected densities; etc.

The present invention may, in one aspect, preferably provide physicianswith the ability to tailor the delivery of drugs within the spinalregion. Tailored delivery of one or more drugs in accordance with thepresent invention may, e.g., increase the therapeutic efficacy of thedrug infused by the system and may also reduce the amount of drug thatreaches other sites in, e.g., the spine or brain (thus potentiallyreducing undesirable side effects).

In accordance with various exemplary aspects of the invention, thedistribution profile of an intrathecally delivered drug solution may bemodified by, e.g., varying the baricity (density) of the solution,changing the concentration or hydrophilicity/hydrophobicity of the drug(e.g., selecting a polymorph form of an agent, acid or base salt orneutral form an agent, etc.; selecting a different suitable agent; etc.)or solution carrying the drug, changing the location within the spinalcord where the drug is infused, changing the infusion rate of the drug,changing a pore size of a permeable membrane through which the drug isinfused, or a combination thereof.

In some embodiments, the present invention may be in the form of a drugdelivery catheter that includes an elongated body with a proximal endand distal end. The catheter includes a lumen extending from theproximal end of the body to an infusion section spaced from the proximalend of the body. The infusion section may preferably include two or moreopenings in a wall of the lumen within the infusion section and apermeable membrane covering the two or more openings in the infusionsection. The two or more openings and the permeable membrane coveringthem may preferably create a back pressure in the lumen such that thedrug exits the infusion section through all of the two or more openingsin the infusion section when a drug is delivered to the infusion sectionthrough the lumen at a continuous rate of 1 milliliter per hour or less.

In connection with the catheters described herein, it may be preferredthat the permeable membrane create a back pressure of 300 pascals ormore in the lumen when the drug is delivered to the infusion sectionthrough the lumen at a continuous rate of 2 microliters per hour.

An alternative manner of characterizing the permeable membrane of thecatheter described in the preceding paragraph may be based on molecularweight cut-off, e.g., where the permeable membrane has a molecularweight cut-off of 80 kiloDaltons or less.

In other embodiments, a drug delivery catheter in accordance with thepresent invention may be described as including an elongated body havinga proximal end and distal end. The elongated body includes a lumenextending from the proximal end of the body to an infusion sectionspaced from the proximal end of the body. The catheter may include oneor more openings in a wall of the lumen within the infusion section anda permeable membrane covering the one or more openings in the infusionsection. The one or more openings and the permeable membrane coveringthem may preferably create a back pressure of 300 pascals or more in thelumen when the drug is delivered to the infusion section through thelumen at a continuous rate of 2 microliters per hour. The permeablemembrane may, e.g., have a molecular weight cut-off of 80 kiloDaltons orless.

In still another embodiment, a drug delivery catheter in accordance withthe present invention may include an elongated body with a proximal endand distal end. A lumen may extend from the proximal end of the body toan infusion section spaced from the proximal end of the body. One ormore openings may be formed in a wall of the lumen within the infusionsection and a permeable membrane may cover the one or more openings inthe infusion section. The permeable membrane may have a molecular weightcut-off of 80 kiloDaltons or less.

In other embodiments, the catheters described herein may be used in drugdelivery systems that include a drug delivery apparatus including a pumpand a reservoir. The drug delivery apparatus may preferably beimplantable within the body of the patient.

Various methods of using drug delivery catheters including permeablemembranes according to the present invention may also be characterizedon the basis of back pressures developed at specified flow rates and/orthe molecular weight cut-off of the permeable membrane. For example,delivering the drug may create sufficient back pressure in the lumensuch that the drug passes through all of the two or more openings in theinfusion section when the drug is delivered to the infusion sectionthrough the lumen at a continuous rate of 1 milliliter per hour or less.In addition, the method may be characterized as creating a back pressureof 300 pascals or more in the lumen when the drug is delivered to theinfusion section through the lumen at a continuous rate of 2 microlitersper hour.

In another method of using a drug delivery catheter according to thepresent invention, delivering the drug may involve creating a backpressure of 300 pascals or more in the lumen when the drug is deliveredto the infusion section through the lumen at a continuous rate of 2microliters per hour.

In still another method of using a drug delivery catheter according tothe present invention, delivering the drug through the infusion sectionmay involve passing the drug out of the infusion section through all ofone or more openings formed through a wall of the lumen within theinfusion section, wherein the drug passes through a permeable membranecovering the one or more openings, and wherein the permeable membranehas a molecular weight cut-off of 80 kiloDaltons or less.

In some embodiments, the drug delivery catheters used in, e.g., systemsof the present invention may include more than one infusion section. Theinfusions sections may be located along the same lumen or differentlumens. It may be preferred that the different infusion sections beseparated along the axial length of the catheter by a distance of, e.g.,20 mm or more. Further, the walls of the lumen may preferably beimpermeable to liquids between the infusion sections such that drugdelivery through the catheter is restricted to the infusion sections.

Spacing between adjacent infusion sections along the length of a drugdelivery catheter may be characterized in a variety of manners. As notedabove, the infusion sections may preferably be separated by an axialdistance of 20 mm or more. In other embodiments, the infusion sectionsmay be separated by, e.g., an axial distance of one human vertebrallevel or more. In still other embodiments, the infusion sections may beseparated by, e.g., an axial distance of 40 mm or more. In otherembodiments, the infusion sections may be separated by, e.g., an axialdistance that is a whole number multiple of one human vertebral level(e.g., 40 mm).

In other embodiments, the catheters including multiple infusion sectionsas described herein may be used in drug delivery systems that include adrug delivery apparatus including at least one pump and at least onereservoir. The drug delivery apparatus may preferably be implantablewithin the body of the patient. It may be preferred that the pump be animplantable pump and the reservoir be an implantable reservoir.

The present invention may also include a method of infusing a drug tomultiple internal body locations by delivering a drug from a reservoirto a first infusion section and a second infusion section of a catheterthrough a lumen, wherein the catheter includes an elongated bodycomprising a proximal end and a distal end. The first infusion sectionand the second infusion section are located along the elongated body,with the second infusion section being located between the proximal endof the elongated body and the first infusion section. The first infusionsection and the second infusion section may be spaced apart from eachother along the elongated body by an axial distance of 20 mm or more.The method may further involve passing the drug out of the lumen throughthe one or more openings in the first infusion section and passing thedrug out of the lumen through the one or more openings in the secondinfusion section.

In still other embodiments, the present invention may provide a drugdelivery catheter having an elongated body with a proximal end and adistal end. A first lumen may extend from the proximal end of the bodyto a first infusion section located along the elongated body which mayinclude one or more openings in the first lumen. The catheter may alsoinclude a second lumen extending from the proximal end of the body to asecond infusion section that is located along the elongated body andthat is spaced apart from the first infusion section along the body byan axial distance of 20 mm or more. The second infusion section maypreferably be located along the elongated body between the proximal endof the elongated body and the first infusion section. The secondinfusion section may also include one or more openings in the secondlumen within the second infusion section.

Spacing between adjacent infusion sections along the length of a drugdelivery catheter including two or more lumens may be characterized in avariety of manners. As noted above, the infusion sections may preferablybe separated by an axial distance of 20 mm or more. In otherembodiments, the infusion sections may be separated by, e.g., an axialdistance of one human vertebral level or more. In still otherembodiments, the infusion sections may be separated by, e.g., an axialdistance of 40 mm or more. In other embodiments, the infusion sectionsmay be separated by, e.g., an axial distance that is a whole numbermultiple of one human vertebral level (e.g., 40 mm).

In other embodiments, the catheters including multiple lumens, each withat least one infusion section as described herein may be used in drugdelivery systems that include a drug delivery apparatus including atleast one pump and at least one reservoir. The drug delivery apparatusmay preferably be implantable within the body of the patient. It may bepreferred that the pump be an implantable pump and the reservoir be animplantable reservoir.

The present invention may also preferably provide methods of deliveringone or more drugs to two or more locations within the spinal region of apatient. Such a method may include delivering a first drug to a firstlocation within the spinal region of a patient; and delivering a seconddrug to a second location within the spinal region of a patient; whereinthe first drug and the second drug are the same or different.

Delivery of the first and second drugs to the first and second locationsmay be performed simultaneously or not. Also, the first drug and thesecond drug may be delivered through the same catheter or differentcatheters. In some instances, the first drug may be delivered through afirst lumen in a catheter and the second drug may be delivered through asecond lumen in the same catheter. The catheters used in such a methodmay include, e.g., any suitable catheters among those described hereinor other catheters that are not described herein.

The present invention may also include an implantable drug deliverysystem that includes an implantable pump assembly and two or moreimplantable reservoirs operably connected to the implantable pumpassembly. The system also preferably includes a catheter connection portadapted to attach a catheter to the drug delivery system and a reservoirswitching valve assembly between the two or more implantable reservoirsand the catheter connection port, wherein the two or more implantablereservoirs can be selectively connected to the catheter connection port.In some embodiments, the reservoir switching valve assembly may beoptional and in such embodiments, it may be desirable to include a pumpassembly that includes, e.g., two or more pump mechanisms.

Such implantable systems may include, e.g., in various embodiments: atelemetry module operably connected to control the reservoir switchingvalve assembly; an implantable density sensor; a telemetry moduleoperably connected to the density sensor; means for mixing fluidsdelivered from at least two of the two or more reservoirs such that amixed fluid having a selected density can be obtained based on, e.g., adensity measured by the density sensor.

In such a system with multiple implanted reservoirs, two reservoirs ofthe two or more reservoirs contain different drugs that may, e.g., be indrug solutions having different densities. In another alternative, tworeservoirs of the two or more reservoirs may contain the same drug intwo different drug solutions having different densities.

Such a system may also incorporate means for modifying the flow rate tothe catheter connection port such as by using an implantable pumpassembly that includes at least one programmable pump mechanism, a flowrestrictor, metering valve, etc.

In a system with multiple implanted reservoirs, it may be preferred touse a catheter that includes, e.g., a first lumen extending from theproximal end of the catheter to a first infusion section and a secondlumen extending from the proximal end of the catheter to a secondinfusion section. Such a system may also preferably include a lumenswitching valve assembly between the two or more reservoirs and thecatheter, wherein the two or more reservoirs can be selectivelyconnected to one or both of the first lumen and the second lumen.

In some embodiments, the system may include dedicated relationshipsbetween reservoirs and catheter lumens. For example, the two or morereservoirs may include a first reservoir connected to the first lumen ofthe catheter and a second reservoir connected to the second lumen of thecatheter. Valves may be used to control flow through each of the lumens.

The present invention may also involve methods of delivering one or moredrugs to at least one internal body location using a drug deliverysystem implanted in the body of a patient, wherein the drug deliveryapparatus includes an implantable pump assembly, two or more implantablereservoirs operably connected to the implantable pump assembly, acatheter connection port adapted to attach a catheter to the drugdelivery system, and a reservoir switching valve assembly between thetwo or more implantable reservoirs and the catheter connection port. Themethod may include, e.g., selectively connecting at least one reservoirof the two or more implantable reservoirs to the catheter connectionport; and delivering a drug from at least one reservoir of the two ormore implantable reservoirs to the catheter connection port using theimplantable pump assembly.

In such a method, the reservoir switching valve assembly may becontrolled from a location outside of the body of the patient. Themethod may involve, e.g., measuring density of the cerebrospinal fluidof a patient using an implanted density sensor.

In other variations, the methods may include mixing fluids deliveredfrom at least two of the two or more reservoirs before delivering thedrug. In some instances, the two reservoirs of the two or morereservoirs contain different drugs in solutions having the same ordifferent densities. In still other instances, two reservoirs maycontain the same drug in two different drug solutions having differentdensities.

In still other potential aspects of the present invention, the cathetersand/or drug delivery systems may be used in methods of adjusting thedensity of a drug solution to be delivered to an internal body locationof a patient. Such methods may involve, e.g., determining a selecteddensity for the drug solution; formulating the drug solution from two ormore components to obtain the selected density for the drug solution,and infusing the drug solution to an internal body location at acontinuous rate of no more than 50 milliliters (ml) per hour for aperiod of five minutes or more. In variations on this method, themaximum infusion rate may be, e.g., no more than 25 ml per hour, no morethan 10 ml per hour, no more than 5 ml per hour, or even potentially nomore than 2 ml per hour. Variations may also be found in the time periodover which the infusion is performed. The period of infusion mayalternatively be, e.g., 10 minutes or more, one hour or more, eighthours or more, or even 24 hours or more.

In still other variations on the methods described in the previousparagraph, the infusing may preferably be performed for a period of atleast 8 hours within a twenty four hour period. Alternatives to this mayinclude, e.g., at least 12 hours within a twenty four hour period, oreven at least 16 hours in a twenty four hour period.

In another manner of characterizing the invention, the infusion processmay be described in terms of a duty cycle, e.g., where the infusion isperformed for a duty cycle of at least 25% within a given time period,or at least 50% within a given time, or even at least 75% within a giventime period. The time periods over which the duty cycle is determinedmay be, e.g., 8 hours or more, 12 hours or more, 16 hours or more, oreven 24 hours or more.

In some methods, determining the selected density involves determiningthe density of the cerebrospinal fluid of a patient either in vivo(using a density sensor located within the cerebrospinal fluid of apatient) or measuring the density of the cerebrospinal fluid afterremoving the cerebrospinal fluid from the patient.

Formulating the drug solution may be performed outside of the body ofthe patient or within the body of the patient (using, e.g., some of thesystems described herein). If the drug solution is formulated within thebody of the patient, it may be desirable to obtain the components forthe drug solution from two or more reservoirs implanted within thepatient.

Because density variations can have an effect on the efficacy of atreatment plan, it may be desirable to obtain feedback regardingefficacy of the drug solution after delivering the drug solution to thepatient. The method may then involve adjusting the density of the drugsolution based on the feedback. The feedback may be provided by, e.g.,the patient, doctors, nurses, other caregivers, sensors, etc.

In another method of adjusting the density of a drug solution, thepresent invention may involve determining a selected density for thedrug solution; and controlling the temperature of the drug solution toincrease or decrease the density of the drug solution to reach theselected density. As discussed above, determining the selected densitymay involve determining the density of the cerebrospinal fluid of apatient either in vivo (using a density sensor located within thecerebrospinal fluid of a patient) or measuring the density of thecerebrospinal fluid after removing the cerebrospinal fluid from thepatient.

To take advantage of the use of drug solution density, it may beadvantageous to employ a drug delivery system that includes a drugdelivery apparatus with a pump assembly and two or more reservoirsoperably connected to the pump assembly. The system may further includea catheter connection port adapted to attach a catheter to the drugdelivery system and means for mixing fluids from at least two reservoirsof the two or more reservoirs at or before delivering the fluids to thecatheter connection port.

Such a system designed to deliver drug solutions with selected densitiesmay include, e.g., an implantable density sensor operably connected tothe drug delivery apparatus.

In a system designed to supply drug solutions with selected densities,two reservoirs of the two or more reservoirs may preferably containdifferent fluids. The different fluids may, e.g., have differentdensities.

In one embodiment, a first reservoir of the two or more reservoirs maycontain a first fluid with a low density, a second reservoir of the twoor more reservoirs may contain a second fluid with an intermediatedensity, and a third reservoir may contain a third fluid with a highdensity (where the low, intermediate and high densities are relative toeach other only). The second fluid may include the drug to be deliveredsuch that addition of the first fluid lowers the density of the drugsolution or addition of the third fluid increases the density of thedrug solution. In some systems, the first fluid and the third fluid maybe substantially free of the drug.

In another variation, at least two fluids of the first fluid, the secondfluid, and the third fluid may include the same drug. In still anothervariation, two reservoirs of the two or more reservoirs may contain thesame drug in two different drug solutions having different densities.

Density control systems may also include a thermal control device forcontrolling the temperature of the drug (in addition to controllingdensity through selective mixing of fluids having different densities).

It may be preferred that the pump assembly be an implantable pumpassembly, and that the two or more reservoirs be implantable reservoirsoperably connected to the implantable pump assembly, and further whereinthe means for mixing is implantable means for mixing.

In another aspect, the present invention may provide a drug deliverysystem that includes a drug delivery apparatus having a pump assembly,one or more reservoirs operably connected to the pump assembly, and acatheter connection port adapted to attach a catheter to the drugdelivery system. The system also includes a thermal control device forcontrolling the temperature of the drug delivered to the patient.

The thermal control device may, e.g., control the temperature of thedrug before the drug is delivered to the catheter connection port.Alternatively, the thermal control device may control the temperature ofthe drug after the drug passes through the catheter connection port. Thethermal control device may be located within a catheter connected to thecatheter connection port. Such a system may also include an implantabledensity sensor operably connected to the drug delivery apparatus. Thedensity sensor may be operably connected to the drug delivery apparatus,whereby a fluid having a selected temperature can be obtained based on adensity measured by the density sensor. Such a system may preferably beimplantable.

These and other features and advantages of the systems and methods ofthe present invention may be described below in connection with someillustrative examples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of one drug delivery system implantedwithin the body of a patient and infusing drug into the brain.

FIG. 1B is a schematic diagram of one implanted drug delivery system forinfusing drug directly to the spinal region.

FIG. 1C is a schematic diagram of one implanted drug delivery system forinfusing drug directly to the peripheral nervous system.

FIG. 2 depicts an enlarged view of a drug delivery system similar tothat depicted in, e.g., FIG. 1B.

FIG. 3 depicts the distal end of the catheter of FIG. 2 infusing druginto the spinal region.

FIG. 4 is an enlarged cross-sectional view of one example of an infusionsection including multiple infusion openings in a catheter used inconnection with the present invention.

FIG. 5 is an enlarged cross-sectional view of another example of aninfusion section including a permeable membrane in a catheter used inconnection with the present invention.

FIG. 6 depicts a catheter including two infusion sections spaced apartalong the axial length of the catheter.

FIG. 7 depicts another drug infusion system according to the presentinvention including a catheter with two lumens and two pump mechanisms.

FIG. 8 is a schematic diagram of another drug delivery system accordingto the present invention including multiple reservoirs for mixing drugsolutions with selected densities or other properties.

FIG. 9 is a schematic diagram of another drug delivery system includingthermal control devices for controlling the temperature of the drugsdelivered to the patient.

FIG. 10 is a schematic diagram of another drug delivery system accordingto the present invention incorporating a variety of optional components.

FIG. 11 is a schematic diagram of another drug delivery system accordingto the present invention incorporating a lumen switching valve assembly.

FIG. 12 depicts a catheter according to the present invention includinga fork and two branches extending therefrom.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

In the following detailed description of illustrative embodiments of theinvention, reference is made to the accompanying figures of the drawingwhich form a part hereof, and in which are shown, by way ofillustration, specific embodiments in which the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural changes may be made without departing from the scope ofthe present invention.

The present invention may be used in connection with a variety ofmethods, catheters and/or systems as may be described in, e.g., U.S.patent application Ser. No. 10/745,897, titled REDUCTION OF INFLAMMATORYMASS WITH SPINAL CATHETERS, filed on Dec. 23, 2003; U.S. patentapplication Ser. No. 10/745,750, titled METHOD OF DELIVERING DRUGS TOSPECIFIC REGIONS OF THE SPINAL CORD, filed on Dec. 23, 2003; U.S. patentapplication Ser. No. 10/745,719, titled TRIALING SYSTEM FOR EVALUATIONOF THE EFFICACY OF THE TREATMENT, filed on Dec. 23, 2003; and U.S.patent application Ser. No. 10/745,731, titled METHOD OF DELIVERING DRUGTO BRAIN VIA THE SPINAL CANAL, filed on Dec. 23, 2003.

The present invention relates to the delivery of drugs. For the purposesof the present invention, the term “drug” means any pharmacological ortherapeutic agent or combination of agents delivered to provide therapyto a patient (human or non-human animals). The drugs will typically beliquids or materials contained in liquid carriers as either solutions ormixtures (although where used herein, the term “solution” refers to bothsolutions and mixtures).

Furthermore, although in many instances, the catheters, drug deliverysystems, methods and other aspects of the invention may be useful inconnection with delivery of one or more drugs to the spinal region, itshould be understood that the present invention may find use inconnection with delivery of one or more drugs to other internal bodylocations as well, including, but not limited to, the brain or any othersuitable anatomical location.

As used herein, the term “spinal region” includes the spinal canal(including the spinal cord, intrathecal space, dura, epidural space,etc.), vertebra, spinal discs, nerve roots, and the ligaments, tendonsand muscles in between and surrounding the vertebra.

Exemplary embodiments of some drug delivery systems for infusing drugsare depicted in FIGS. 1A, 1B, and 1C. FIG. 1A is a schematic diagram ofa drug delivery system for infusing drug to the brain, FIG. 1B is aschematic diagram of a drug delivery system for infusing drug to thespinal region, and FIG. 1C is a schematic depiction of a drug deliverysystem for infusing drug to the peripheral nervous system.

The drug delivery systems depicted in FIGS. 1A and 1B includes a druginfusion pump assembly 10A/10B and catheter 20A/20B having a proximalend 22A/22B attached to the pump assembly and distal end 24A/24Bimplanted within the patient. The distal end 24A is implanted within thebrain 30A of the patient, while the distal end 24B is implanted withinthe spinal column 30B of the patient.

FIG. 1C depicts only a portion of the drug delivery system, namely theportion of catheter 20C including its distal end 24C, which is implantedto infuse drugs to the peripheral nervous system. The depicted infusionsite in the arm is provided as exemplary only, with the systems of thepresent invention capable of infusing drugs to any internal bodylocation.

Furthermore, although the systems of FIGS. 1A, 1B, and 1C are depictedinfusing drugs into only one area, e.g., brain, spinal region orperipheral nervous system, it should be understood that a single systemcould infuse one or more drugs to one or more locations in any one ormore of the brain, spinal region and/or peripheral nervous system. Also,although depicted in connection with a human body, it should beunderstood that the drug delivery systems of the present invention couldalso be used on non-human animals.

The pump assembly 10 may preferably be surgically implantedsubcutaneously in the pectoral or abdominal region of the subject'sbody. The pump assembly 10 may be any suitable mechanism capable ofdelivering one or more drugs to a patient. The pump assembly 10preferably includes a pumping mechanism, at least one reservoircontaining the drug to be delivered, and a power supply to operate thepump assembly 10 such that the drug is delivered to the patient at aselected rate. Examples of some suitable pumps may include, e.g.,commercially available implantable infusion pumps such as, for example,the SYNCHROMED EL pumps, Models 8626 and 8627, manufactured byMedtronic, Inc., Minneapolis, Minn. It should be understood that somepumps used in connection with the present invention may not require aseparate power supply.

While an implantable pump assembly 10 is depicted, it should beunderstood to those skilled in the art that the device used to deliverdrug to the catheter may be either implanted or extracorporeal. As usedherein, the term “implantable” means that the system, apparatus ordevice is adapted for implantation in the body of subject where it islocated at least subcutaneously.

One exemplary structure of a pump assembly 10 and catheter 20 may beunderstood by reference to FIG. 2, which depicts one embodiment of thesystem with a portion of the catheter 20 shown in an enlarged halfsection. The size of the catheter 20 is exaggerated for ease ofillustration of the structure thereof and the full length of thecatheter 20 is not shown for simplicity of illustration. The proximalend 22 of the catheter 20 is coupled to the pump connector 12. Theconnection between the catheter 20 and the pump connector 12 is shownschematically in FIG. 2. It should be understood that the actual type ofconnection between the pump connector 12 and the catheter 20 will varydepending upon the particular type of pump assembly 10 utilized.

The catheter 20 includes an elongated tubular portion 23 that preferablyextends from the proximal end 22 to the distal end 24. The catheter 20depicted in FIG. 2 includes a lumen 26 that terminates at opening 28 atthe distal end 24. Drug delivered from the pump assembly 10 to thecatheter 20 passes through lumen 26 and exits the catheter throughopening 28.

When implanted for delivering drugs to, e.g., the spinal region, it maybe preferred that at least a portion of the catheter 20 be locatedwithin the CSF of the patient such that as drug exits the catheter 20 itenters directly into the CSF. By “directly,” it is meant that the drugpreferably does not contact other tissues or bodily fluids beforereaching the CSF of the patient.

The body of catheter 20 may preferably be constructed of any suitablematerial, e.g., an elastomeric tube. If used in the spinal canal, thecatheter 20 may be floating free in the CSF and may contact the spinalcord. As a result, in such an application the catheter 20 may preferablybe soft and flexible to limit any chance of damaging the spinal cord.Examples of some suitable materials include, but are not limited to,silicone rubber (e.g., polydimethyl siloxane) or polyurethane, both ofwhich can provide good mechanical properties and are very flexible.Suitable materials for the catheter 20 are also preferably chemicallyinert such that they will not interact with drugs or body tissue or bodyfluids over a long time period.

In some embodiments, the catheter may preferably be sized to fit in thegap between the spinal cord 32 and the dura 36 (see, e.g., FIG. 3). Theinside diameter, e.g., the diameter of the lumen 26, is preferably largeenough to accommodate expected infusion rates with acceptable flowresistance. The wall 21 of the catheter 20 is preferably thick enough towithstand normal handling during the implant procedure and forces frombody tissues during normal motion. As an example, the catheter 20 mayhave an outside diameter of 1.25 millimeters (mm) and an inside diameterof 0.5 mm, with a wall thickness of 0.375 mm. The catheter 20 may be,e.g., 50 centimeters (cm) long to reach from, e.g., a drug infusion pumpimplanted in the patient's abdomen to the spine.

FIG. 3 depicts catheter 20 positioned within a schematic representationof a spinal canal 30. The spinal canal 30 includes the spinal column 32which terminates at the cauda equina 34. Also depicted is the dura 36which contains the cerebrospinal fluid (CSF) that surrounds the spinalcolumn 32. The catheter 20 is positioned such that the distal end 24 ofthe catheter 20 is located within the volume occupied by the CSF.

In the embodiment depicted in FIGS. 2 & 3, the catheter 20 includes onlyone opening 28 at the distal end 24 of the catheter 20. As a result,drugs delivered to the CSF through catheter 20 will exit through theopening 28 in the distal end 24 of the catheter 20. If the density ofthe drug so delivered is lighter than the CSF into which the drug isdelivered, then the drug may form a plume 40 as seen in FIG. 3 in whichthe drug rises from the delivery point.

Many alternatives may be provided for the structure through which thedrug passes out of the catheter. The catheter 20 including an opening 28at its distal end 24 is only one example. FIG. 4 depicts a section ofone alternative design in which the catheter 120 includes multipleopenings 128 formed through the wall of the catheter 120 within aninfusion section 127. As drug moves through the lumen of the catheter120, it exits through the openings 128. In such an embodiment, it may bepreferred that the distal end of the catheter 120 be closed such thatthe drug exits through openings 128 in the catheter wall. The size andspacing of the openings 128 may vary depending on a variety of factorssuch as, e.g., viscosity of the drug being delivered, desired deliveryrate, etc.

The axial length of the infusion section 127 (as measured along an axisextending from the proximal to the distal end of the catheter) may beselected based on a variety of factors. For example, to control pain,the pain signals can be blocked by appropriate analgesic drugs in thedorsal nerve roots or in the spinal cord. Nerve roots do not have asingle junction with nerve cells in the spinal cord, but split into manybranches in both directions. To block a substantial number of painsignals, the drug may preferably be delivered over several vertebrallevels above and below the affected nerve root. As an example, theinfusion section may be constructed to cover three vertebral levels,e.g., the affected nerve root entry level and one vertebral level aboveand below. Each vertebral segment in a human adult is approximately 40mm long, and, as a result, the infusion section could be, e.g., 80 mmlong.

The length of infusion section 127 over which the openings 128 aredispersed may, in some embodiments, preferably have a limited axiallength of, e.g., 320 millimeters (mm) or less, in some instances 160 mmor less, or even 120 mm or less. At the lower end of the range, it maybe preferred that the infusion section 127 have an axial length of 20 mmor more, possibly 40 mm or more.

FIG. 5 depicts another potential construction for the infusion section227 of a catheter 220 in an enlarged cross-sectional view. The depictedinfusion section 227 includes openings 228 formed in the lumen 226,e.g., through the wall 221 of the catheter 220. The distal end 224 ofthe catheter 220 may preferably include a plug 229 or be closed in someother manner.

Unlike catheter 120 depicted in FIG. 4, infusion section 227 of catheter220 includes a permeable membrane 225 through which any drugs passingout of catheter 220 must pass. The permeable membrane 225 may beprovided as seen in FIG. 5, e.g., as a hollow tube located within lumen226 of the catheter 220 that is positioned to cover openings 228 suchthat any drug must pass through the permeable membrane before passingthrough openings 228. Alternative constructions could include apermeable membrane over the outside of the catheter or plugs of apermeable membrane located within the openings themselves.

In the depicted configuration, the tubing of the catheter 220 maypreferably provide mechanical support for the permeable membrane 225 andmay also preferably provide protection from damage for the permeablemembrane 225.

The permeable membrane 225 may preferably be provided in the form of ahollow fiber similar to those used in, e.g., blood oxygenators or kidneydialysis systems. Hollow fiber permeable membranes may be made from anumber of different materials that preferably do not chemically interactwith the drugs to be delivered and are biocompatible, e.g.,polyurethane, silicone rubber, polyimide, polyethylene, polysulfone, orpolyethersulfone.

In the depicted embodiment, the outside diameter of the hollow fiberpermeable membrane 225 may be the same as the inside diameter of thecatheter lumen 226 such that the permeable membrane 225 may be retainedin the selected location by friction. Alternatively, the permeablemembrane 225 may be held in place by any other suitable technique ortechniques, e.g., adhesives, thermal welding, chemical welding, etc.Furthermore, although the depicted permeable membrane 225 is provided inthe form of a hollow fiber, the permeable membrane 225 may be providedin any other suitable form, e.g., a plug occupying the lumen 226, sheet,etc.

The openings 228 within the infusion section may be arranged in anydesired manner, e.g., linearly along the axis of the catheter 220, in aspiral around the axis, a series of circumferential circles, etc.Locating the openings 228 on one side of the catheter 220 may bebeneficial in, e.g., distributing the drug as described herein. As oneexample, the infusion openings may be, e.g., 0.05 mm in diameter, with,e.g., ten to twenty holes distributed over the infusion section 227.

As compared to spinal catheters with one or multiple infusion openingsas depicted in FIGS. 2 and 4, a spinal catheter 220 having a permeablemembrane 225 may offer a number of potential advantages. For example, ifthe pump used to deliver drug through a catheter having an infusionsection with multiple holes and no permeable membrane is programmed todeliver the drug at a low rate (e.g., 0.5 milliliters (ml) per day), thedrug may exit only through a single infusion opening, typically theopening that is closest to the pump. This may occur because the infusionopenings are so large that no back pressure is built up in the catheterat the low infusion rates to force the infusate to reach all of theholes.

If, however, a permeable membrane 225 with sufficiently small pore sizesis used, a back pressure of drug may be built up in the catheter lumen226 that is large enough to distribute the drug over the entire lengthof the infusion section 227 such that the drug passes through all of theopenings 228 in the infusion section 227.

In one manner of characterizing some catheters of the present invention,the openings 228 and the permeable membrane 225 covering them within theinfusion section 227 may preferably create a back pressure in the lumen226 such that the drug exits the permeable membrane 225 through all ofthe openings 228 in the infusion section 227 when a drug is delivered tothe infusion section through the lumen 226 at a continuous rate of 1milliliter per hour or less.

In another manner of characterizing some catheters of the presentinvention, the openings 228 and the permeable membrane 225 covering themwithin the infusion section 227 may preferably create a back pressure300 pascals or more in the lumen when the drug is delivered to theinfusion section through the lumen at a continuous rate of 2 microlitersper hour. Even at such a low back pressure, the permeable membrane 225may preferably cause the drug to pas through all of the openings withinthe infusion section 227 to enhance uniform delivery of the drug overthe infusion section 227.

The permeable membrane (whether in the form of a hollow fiber or someother shape) may be provided with a variety of pore sizes. The membranepore size may be characterized in terms of Molecular Weight Cutoff(MWCO), typically the largest size molecule that will pass through themembrane. More specifically, MWCO of a permeable membrane refers to amembrane through which 90% of a substance having a particular molecularweight can pass under certain test conditions. That is, a membranethrough which 90% of a permeate having a molecular weight of 80 kDapasses would be determined to have a MWCO of 80 kDa. Permeates usefulfor determining molecular weight cutoff include dextran T-fractions andalbumin. The amount of permeate that passes through a membrane may bedetermined by comparing HPLC data regarding a solution containing thepermeate before being applied to the membrane and after passing themembrane. HPLC analysis is useful because a calibration curve of elutiontime versus molecular mass may be produced. Thus, the amount andmolecular weight of permeate passing through the membrane may bedetermined by comparison to the calibration curve. This method ofmeasurement is typically used by filter manufacturers for filter poresizes smaller than 0.1 micrometer (μm). In connection with the presentinvention, it has been found experimentally that a permeable membranewith a molecular weight cutoff of 80,000 Daltons or less may preferablybe used to achieve the desired infusion characteristics.

When characterized in terms of back pressure developed within the lumen,it may be preferred that the back pressures and/or flow rates are fordrug solutions that may preferably have, e.g., a viscosity of water orhigher at, e.g., basal body temperatures or the temperatures at whichthe drug solutions are delivered.

In addition to generating the desired back pressure, permeable membraneswith these pore sizes may preferably cause the drug exiting the catheterto form droplets that may preferably be small enough to be rapidlydiluted into, e.g., CSF and form a diffuse cloud at the infusion site.Suitable hollow fiber permeable membranes may be obtained from, e.g.,Minntech Corporation (Minneapolis, Minn.), Spectrum Laboratories, Inc.(Rancho Dominguez, Calif.), Membrana GmbH (Wuppertal, Germany), etc.

One method of manufacturing a catheter 220 with an infusion section 227including a hollow fiber permeable membrane 225 as seen in, e.g., FIG. 5may involve inserting the hollow fiber permeable membrane 225 in thelumen 226 of the catheter 220 and retaining the membrane 225 in positionwith friction. In one method of providing a friction fit, the hollowfiber 225 may have an outside diameter that is slightly larger than theinside diameter of the lumen 226, e.g., the hollow fiber 225 may have anoutside diameter of 0.6 mm to fit inside a lumen with an inside diameterof 0.5 mm. If the catheter 220 is manufactured of, e.g., silicone,polyurethane, etc., the lumen 226 may be temporarily swelled by soakingin, e.g., ethyl alcohol. While the lumen 226 is swollen, the hollowfiber 225 may be placed in the lumen 226. As the alcohol evaporates outof the tubing used for catheter 220, the tubing will shrink to itsoriginal dimensions, preferably holding the hollow fiber permeablemembrane 225 in position by frictional forces.

Another optional feature that may be provided in connection with thepresent invention is depicted in the cross-sectional view of FIG. 6. Thecatheter 320 includes two separate infusion sections 327 a and 327 b(collectively referred to herein as “infusion sections 327”) spacedapart from each other along the axial length of the catheter 320. Asdiscussed herein, the spacing between separate infusion sections ismeasured between the ends of the infusion sections 327 a and 327 b. Inthe case of infusion sections that include openings such as depicted inFIG. 6, the ends of the infusion sections are determined by the openings328 in the two different infusion sections. For example, the spacing ofthe infusion sections 327 a and 327 b in FIG. 6 would be determined bythe lowermost opening 328 in infusion section 327 a and the uppermostopening 328 in infusion section 327 b. It may be preferred that thelumen is impermeable to liquids between any successive pair of infusionsections such as infusion sections 327.

It should be noted that catheters according to the present inventionthat include two or more infusion sections may preferably include atleast two such infusion sections, e.g., infusion sections 327, along oneaxial length of an elongate body as seen in FIG. 6 such that at leastone infusion section is located between another infusion section and theproximal end of the body on which the infusion sections are located.This is in contrast to, e.g., previously known branched catheters inwhich each branch contains one infusion section, such that any one ofthe axial lengths defined by such a catheter includes only one infusionsection (see, e.g., International Publication No. WO 02/07810 A2(Elsberry et al.)) with no infusion sections located between theproximal end of the catheter and another infusion section.

The axial distance between the different infusion sections 327 may beselected based on a variety of factors such as, e.g., the distancebetween anatomical features to which a drug is to be delivered. Forexample, it may be preferred that the infusion sections 327 be separatedby the distance of one human vertebral segment (e.g., 40 mm) or more. Insome instances, it may be preferred that the infusion sections be spacedapart from each other by an axial distance that is a whole numbermultiple of one average human vertebral level (e.g., 40 mm).

Each of the infusion sections 327 may preferably include a permeablemembrane 325 and one or more infusion openings 328. Because the infusionsections 327 are displaced from each other, it may be preferred to useseparate permeable membranes 325 in each of the infusion sections 327.The separate permeable membranes 325 may have the same or differentphysical properties (e.g., MWCO values, materials, etc.) In someinstances, however, a single unitary permeable membrane may extendbetween different infusion sections 327. Also, although FIG. 6 depictsonly two infusion sections 327, it will be understood that catheters ofthe present invention may include more than two separate infusionsections, e.g., three or more infusion sections.

As for one potential use for a catheter having more than one infusionsection, a patient may have chronic pain symptoms from more than onecause or in more than one location. For such a patient, it may bedesirable to deliver analgesic drugs in more than one location along thespinal cord to reach all appropriate synapses. For example, one infusionsection could be located proximate the spinal cord at a higher vertebrallevel, so that the drug will preferably diffuse to the dorsal horn.

Still another drug delivery system that may be used in connection withthe present invention is depicted in FIG. 7. The catheter 420 (depictedin cross-section) includes two infusion sections 427 a and 427 b(collectively referred to herein as “infusion sections 427”). Unlikecatheter 320 of FIG. 6 in which a single lumen services both infusionsections 327, however, each of the infusions sections 427 of catheter420 is serviced by a separate lumen 426 a or 426 b.

Even though serviced by separate lumens 426 a and 426 b, however, theinfusion sections 427 can still be characterized as including onesection 427 b that is located between the proximal end of the catheter420 (i.e., the end attached to pump assembly 410) and the other infusionsection 427 a along the axial length of the body of the catheter 420.

In such an embodiment, the catheter 420 may be used to, e.g., delivertwo different drugs to different locations along the length of thecatheter 420 (the different locations being identified by the locationof the different infusion sections 427). Alternatively, the catheter 420may be used to deliver the same drug to two different locations atdifferent times and/or for different periods of time. It will beunderstood that although only two lumens and infusion sections aredepicted, devices and methods of the present invention may involvecatheters with three or more lumens, three or more infusion sections andassociated and pump assemblies.

Also, although two infusion sections 427 and two lumens 426 a and 426 bare depicted in connection with the embodiment of FIG. 7, it will beunderstood that catheters of the present invention may include more thantwo infusion sections and/or more than two lumens to service thedifferent infusion sections. Although not depicted, for example, one (orboth) of the infusion sections 427 could be serviced by two or moreseparate lumens such that two or more different drugs could be deliveredby the same infusion section at the same or different times. Forexample, infusion section 427 a could be serviced by two lumens in placeof the single lumen 426 a depicted in FIG. 7.

A schematic diagram of one pump assembly 410 that may be used inconnection with a catheter 420 is seen in FIG. 7. The pump assembly 410may include, e.g., multiple pump mechanisms 410 a and 410 b that are,respectively, preferably connected to lumens 426 a and 426 b. Such asystem may be useful if the two different pump mechanisms 410 a and 410b are to be operated independent of each other. In some other systems,it may be sufficient to provide a single pump mechanism including two ormore reservoirs with different drug solutions. In such a system, thereservoirs may be dedicated to a particular lumen or a switching valveassembly may be used to deliver drug solution from either reservoir toeither or both of the lumens 426 a and 426 b as desired.

Among the methods of the present invention, it may be beneficial toexploit the natural tendencies of liquids to move relative to each otherin response to gravitational and other forces. For example, becausehumans sit and stand in an upright position when awake, drugs deliveredto the CSF may rise or fall in the spinal canal due to buoyancy. Buoyantforces may move the drug more rapidly than diffusion processes cause thedrug to spread radially. Drugs that are more dense than CSF may tend tofall (i.e., move towards the cauda equina) and drugs that are less densethan CSF will rise (towards, e.g., the brain). Density of fluids may bedescribed in terms of baricity. Drugs (or solutions carrying the drugs)may be described relative to the CSF of a patient as being hypobaric(e.g., less dense than CSF and, therefore, tending to rise in CSF) orhyperbaric (e.g., more dense than CSF and, therefore, tending to fall inCSF). The drug may also be described as isobaric (e.g., have neutralbaricity, i.e., the same density as CSF) and, therefore, neither tendingto rise or fall within the CSF.

Thus, if a patient is not responding to a particular therapy because acatheter is delivering a drug to a location that is too high in thespinal column, a drug solution having an increased density may beintroduced to allow the drug to drop to a level of the spinal columnwhere the drug may be more effective in treating the patient. If apatient is not responding to a particular therapy because a catheter isplaced too low in the spinal column, a drug solution having decreaseddensity may be introduced to allow the drug to rise to a level of thespinal column where the drug may be more effective in treating thepatient. The catheter may also be repositioned to more effectivelydeliver the drug to a more desired region of the spinal cord.

If it is desired to have a drug reach a selected region of a spinal cordin roughly proportional concentrations across the particular region, itmay be desirable to infuse the drug through a permeable membrane suchthat the drug may readily mix with CSF and diffuse throughout theparticular region in roughly equal concentrations.

In some methods according to the present invention, the density of thedrug solution may be adjusted before the drug solution is delivered tothe pump apparatus. In such a system the density of the patient's CSFmay be known (within a range of biologically expected values) or theactual density of the CSF may be determined by, e.g., drawing a sampleand determining the density of the sample. The density of the drugsolution may be adjusted relative to the expected or measured density ofthe CSF and a drug solution with a selected density can be supplied inthe pump apparatus for delivery to the CSF by infusion.

In a variation on the above example, a system may be supplied thatincludes the same drug in two or more different solutions that havedifferent densities relative to the density of the CSF. Referring to,e.g., FIG. 7, the two pump mechanisms 410 a and 410 b may be loaded withthe same drug in solutions having two different densities. As a result,the same drug may be delivered to the CSF with different densities basedon, e.g., the measured density of the patient's CSF, a desireddistribution profile, etc. The different drug solutions may be deliveredto either of the infusion sections 427 a and/or 427 b as desired.

In one variation on this method, different drug solutions with same ordifferent densities may also be supplied in the reservoirs of each ofthe different pump mechanisms 410 a and 410 b. For example, it may bedesirable to use more than one analgesic drug to treat multiple types ofpain. For example, nociceptive pain, caused by stimulation ofneurosensors, will typically respond to an opioid such as morphine, butneuropathic pain caused by damage to nerve cells will typically respondbetter to a local anesthetic such as BUPIVACAINE. One method ofcombining more than one drug is to simply mix them in the reservoir ofan implantable drug pump and infuse the mixture through a catheter.

In some cases, however, it may be preferred to deliver the differentdrugs separately to different locations. The system of FIG. 7 may beused to accomplish this method because catheter 420 has two separatelumens 426 a and 426 b and separate infusion sections 427 a and 427 b atdifferent locations on the catheter 420. For example, BUPIVACAINE couldbe infused through the first lumen 426 a such that it is infusedproximate the lumbar nerve roots. A second drug, e.g. morphine, may beinfused through the second lumen 426 b at, e.g., a location proximatethe spinal cord at a higher vertebral level, so that the drug willpreferably diffuse to the dorsal horn the dorsal horn which is at ahigher, thoracic level in the spinal canal.

Although it may be beneficial to use a system in which one or more drugsolutions are formulated outside of the patient to have a selecteddensity, it may be beneficial to mix or formulate drug solutions havingselected densities on-board the pump assembly. By mixing the drugsolutions on-board the pump assembly (which may preferably be implantedin the body of the patient), a level of control may be achieved that isnot possible in known systems.

One exemplary pump assembly 510 that may be used in connection with thepresent invention to take advantage of the buoyant forces to achievesome desired drug distribution profile is depicted in FIG. 8 (as aschematic block diagram for simplicity). The pump apparatus 510 includesa connector 512 for connection to a catheter 520. The catheter 520 maypreferably include one or more lumens that each feed one or moreinfusion sections 527 a and 527 b as discussed herein.

The depicted pump apparatus 510 includes multiple reservoirs 514, 515,516, 517, and 518. The reservoirs 514, 515, 516, 517, and 518 maycontain the same fluids or different fluids, although it may bepreferred that at least one of the reservoirs contain at least one drugfor delivery to the patient. The other reservoirs may contain fluidsthat are designed to allow the user to manipulate the density of thedrug solution delivered through the catheter. For example, reservoir 515may contain a hypobaric liquid (e.g., water), reservoir 516 may containa hyperbaric liquid (e.g., glucose solution), and reservoir 517 maycontain a neutral liquid (e.g., saline). When combined with, e.g., afirst drug in reservoir 514 in various fractions, the density of thedrug solution delivered through the catheter 520 can be adjusted toachieve a desired density or baricity with respect to the CSF.Similarly, reservoir 518 may include, e.g., a second drug that may alsobe delivered to the catheter 520 in selected densities. In still othervariations, two or more of the reservoirs may contain the same drug, butin solutions having different densities.

The depicted pump apparatus 510 includes optional means for mixing 513 aand 513 b to mix the various components of the drug solutions beforedelivery to the connector 512 and attached catheter 520. The means formixing 513 a and 513 b may be provided in a variety of forms, e.g., asmixing chambers, mechanical agitators, vibrating components, staticmixers, etc, and combinations thereof. In another alternative, thevelocity at which the components are delivered to, e.g., the means formixing 513 a and 513 b, the connector 512, and/or the catheter 520 maybe increased to enhance mixing. Furthermore, the means for mixing may beincorporated into the catheter 520 itself.

Each of the reservoirs may also preferably be operably connected to arefilling port 514 p, 515 p, 516 p, 517 p, and 518 p such that thedifferent reservoirs can be refilled. The ports may be located in onecommon septum or in different septums at different locations on the bodyof the pump apparatus. A variety of techniques may be used to ensurerefilling of the selected reservoir. For example, the ports may acceptdifferently sized or shaped needles, the ports may be located in knownpositions and a template may be placed on the patient's skin to assistin refilling, etc.

By providing a variety of drugs and liquids as in pump apparatus 510,the density of the drug solutions delivered to the CSF may be adjustedto, e.g., mix a drug solution that is isobaric (i.e., neutral density)with respect to the CSF, mix a drug solution that is hyperbaric (i.e.,less dense) as compared to the CSF, and mix a drug solution that ishypobaric (i.e., more dense) as compared to the CSF. Furthermore, thedensity of the drug solution can be adjusted during delivery, i.e., itmay be changed to adjust to changes in the density of the CSF and/or toachieve a desired density profile. For example, a hyperbaric drugsolution may be delivered followed by delivery of a hypobaric drugsolution (or vice versa) to deliver drug over a wider region of thespinal canal.

Where the pump apparatus 510 includes two different drugs, it will beunderstood that a similar system could be provided that includes onlyone drug. Other variations may be provided in catheter 520 which mayinclude, e.g., one or more lumens, one or more infusion sections, etc.

One optional feature that is depicted in connection with FIG. 8 is thatcatheter 520 may include a density sensor 550 such that the actualdensity of the CSF may be measured. Density sensors may be manufacturedusing, e.g., microelectromechanical sensor (MEMS) technology in the formof a beam or float configuration. See, e.g., Costello et al., “Densityand Viscosity Sensing with Ultrasonic Flexural Plate Waves,” Proceedingsof Transducers '93, 7^(th) International Conference on Solid-StateSensors and Actuators, Yokohama, Japan, June 1993, Institute ofElectrical Engineers, Japan, pp. 704-707. Such devices may beincorporated in the delivery catheter 520 as depicted or, alternatively,a separate device may be located in the CSF to measure CSF density.

If the actual density of the CSF is measured, that information can befed back into the pump assembly 510 such that the formulation of thedrug solution or solutions can be adjusted to achieve a desired densityrelative to the CSF density. Such measurements and/or adjustments may bemade continuously or at different times as desired using, e.g., openloop or closed loop control systems and methods.

In spite of the density of the drugs as discusced above, drugs may bedelivered to the CSF in a manner that results in essentially neutralbuoyancy even though the drug itself may be hypobaric or hyperbaric withrespect to CSF. For example, if a permeable membrane is used to deliverthe drug, the droplets or particles of drug exiting from the membranemay be so small as to result in a drug-CSF mixture that has a densityclose to pure CSF, thus reducing buoyant forces on the drug. The drugmay then remain in the area of infusion, and diffusion will expand thedrug into a cloud radially.

It should also be understood that although buoyant forces may play arole in drug movement and/or diffusion, the CSF itself is undergoingoscillation and bulk flow that may sometimes overcome the effects ofbaricity, e.g., causing hyperbaric drugs to rise and/or hypobaric drugsto fall in the spinal column.

Other factors that may play a role in the diffusion of drugs within thespinal canal include, e.g., the rate of infusion, drug distributionpatterns between the different compartments of the spinal canal, whetherthe drugs are hydrophilic or lipophilic, the temperature of the drug atthe time of infusion, etc.

With respect to the rate of infusion, low rates of infusion may tend toyield more equitable drug distribution radially for both hypobaric andhyperbaric drugs. Faster flow rates may lead to broader drugdistribution over more vertebral segments than slower flow rates. Assuch, if it is desirable to reach a variety of levels of a spinal columnwith drug, the flow rate with which the drug is delivered may beincreased. In such circumstances, it may be desirable to decrease theconcentration of a drug to be delivered. If it is desired to have a druglocalized to a region around a particular level of the spinal column,the flow rate with which the drug is delivered may be decreased. In suchcircumstances it may be desirable to increase the concentration of thedrug within the solution delivered through the catheter.

It may also be desirable to infuse a drug in discrete intervals in whicha bolus of drug is delivered followed by an interval in which little orno drug is delivered through the catheter (as opposed to a continuousdelivery infusion). Such non-continuous delivery modes may also beuseful to modify the distribution profile of a drug within the spinalcolumn.

In addition, bolus or non-continuous delivery of a drug may provideother advantages in the management of the body's response to infusion ofa drug. For example, such a delivery method may be helpful in reducingthe incidence of inflammatory masses at the infusion site. Inparticular, the systems and methods of the present invention may behelpful in addressing this issue because the site at which the drug isdelivered may be periodically changed (using, e.g., multiple infusionsites). In addition, by adjusting the density of the drug solution,various distribution profiles for the infused drug may be obtained thatcould reduce the incidence of inflammatory masses (e.g., alternatingbetween hypobaric and hyperbaric drug solutions). Also, using systemsthat deliver two or more different drugs may also be used to address theincidence of inflammatory masses by alternating delivery between thedifferent drugs to ameliorate the inflammatory response to continuousdelivery of the same drug. Still another manner by which the catheters,systems and methods of the present invention may reduce inflammatorymasses is by reducing drug density in e.g., CSF or other fluids, fordrugs passed through a permeable membrane during delivery (which canreduce the size of any one droplet of the drug by the relatively smallpore sizes of the permeable membranes).

As noted above, drug distribution patterns between the differentcompartments of the spinal canal may also be considered in connectionwith the present invention. In some instances, it may be desirable toplace the infusion section or sections of the catheter in one or moreselected locations in the spinal region.

The spinal canal is, however, not an open channel, but has severalstructures that divide the canal into separate channels. The dorsalnerve roots, ventral nerve roots, dentate ligaments, and septum posticumare typically present over the length of the spinal cord. They can actas barriers to even distribution of a drug around the circumference ofthe spinal cord. As a result, it may be desirable to locate an infusionsection on a catheter in, e.g., a dorsal location, ventral location,etc. with respect to, e.g., the spinal cord.

For example, sensory signals, including pain signals, are transmittedinto the spinal cord through the dorsal roots. The first synapse islocated in the dorsal horn. It may be preferred, e.g., to locate aninfusion section of a catheter on the dorsal side of the spinal cord toget the most drug (e.g., an analgesic drug) into the synapses in thedorsal horn. Motor signals are transmitted out through the ventralroots. Movement disorders may be controlled by enhancing the excitatoryor inhibitory signals from the brain before the signals are transmittedto the ventral roots. In this case, it may be desirable to locate thecatheter on the ventral side of the spinal cord and get the most druginto the ventral synapses.

Catheters of the present invention may, e.g., be inserted into thespinal region at a level below the end of the spinal cord and thenthreaded up to the desired level. The catheters may, however, be verylimp, making it difficult or impossible to steer the catheter into aspecific area of the spinal region. A guidewire may be used to stiffenthe catheter during placement. The guidewire is then typically removedbefore the catheter is used to infuse drugs. The catheters of thepresent invention may include a guidewire lumen to receive theguidewire.

The guidewire may preferably have a bent tip so that the catheter andguidewire can be guided in a specific direction within the spinalregion. Fluoroscopy or X-rays can be used to visualize the catheterduring placement, and the guidewire rotated until the bend forces it tomove in the desired direction. Catheters including guidewire lumensand/or bent tip guidewires may be described in, e.g., U.S. Pat. No.4,811,743 (Stevens); U.S. Pat. No. 5,003,989 (Taylor et al.); and U.S.Pat. No. 6,512,957 B1 (Witte).

Although the catheters, systems and methods of the present invention maybe useful for infusing drugs to the CSF, there are other neurologicalapplications where the present invention may be useful. One examplewould be to deliver drugs to other areas within the spinal region, forexample, when the site of back pain can be localized to a disc, bone,muscle, or ligament in the spin, a mixture of a steroid and a localanesthetic can be delivered to reduce swelling and reduce pain. Theinfusion sections of catheters according to the present invention maypreferably deliver drug to the entire structure, rather than deliveringdrug at a single point and depend on diffusion and convection to coverthe entire area.

Another example would be delivering drugs into the brain. Functionalareas in the brain are three-dimensional structures, not a single point.Clinical examples include delivering a chemotherapy agent to a tumor anddelivering dopamine to the putamen for treatment of Parkinson's Disease.In yet another example, seizure activity in epileptic patients can belocalized to a region in the thalamus or cerebral cortex. Ananti-convulsant can be delivered to this region to terminate a seizureor to prevent further seizure activity. Again, a catheter with apermeable membrane may provide better organ coverage than deliveringdrug at a single point.

Yet another example would be a neurological disorder in a specific limb,such as an arm or leg. An example would be pain due to neuropathy causedby diabetes. The pain could be reduced by delivering a local anesthetic(and potentially a steroid) to a main trunk of the nerve that has beenaffected. The catheter with a permeable membrane could be surgicallyplaced alongside the nerve, and infuse drug over a length of the nerve.The anesthetic may preferably cover a larger area of the nerve and belocalized to the specific nerve, rather than deliver the drug at a pointand depend on diffusion and convection to distribute the drug. FIG. 1Cdepicts a catheter placed next to a peripheral nerve in the arm. Itshould be recognized that these are only examples; other organs anddisease states could also benefit from the use of this catheter.

Another drug distribution factor to consider in connection with thepresent invention is whether the drug is hydrophilic or lipophilic.Although not wishing to be bound by theory, it is theorized thathydrophilic drugs may have a wider distribution profile than lipophilicdrugs. Accordingly, if it is desirable to reach a variety of levels of aspinal canal with a drug, it may be desirable to select and/or formulatea drug with hydrophilic properties. Alternatively, if it is desired tohave a drug localized to a region around a particular level of thespinal cord, a drug having more lipophilic properties may be selected.

Drug distribution within the spinal canal may also be affected bycontrolling the temperature of the drug as delivered to the spinalcanal. For example, heating the drug solution may make that solutionmore hypobaric (e.g., less dense) and/or cooling the drug solution maymake it hyperbaric (e.g., more dense). FIG. 9 depicts a system in whichthe pump assembly 610 includes a thermal control device 660 to adjustthe temperature of the drug solution before delivery to the catheter620. In addition to or in place of thermal control device 660, thecatheter 620 may include a thermal control device 662. Suitable thermalcontrol devices may be, e.g., electrical resistance heaters, Peltierdevices, etc.

FIG. 10 is a schematic diagram of another drug delivery system accordingto the present invention. The system 700 includes a pump assembly 710(preferably implantable), catheter connection port 712, and tworeservoirs 714 and 715 (preferably implantable). The reservoirs 714 and715 are connected to the pump assembly 710 through a reservoir switchingvalve assembly 770 that is capable of selectively connecting thereservoirs 714 and 715 to the port 712.

Also depicted in FIG. 10 is a controller 702 for operating one or morecomponents of the system 700. The controller 702 may be, e.g., amicroprocessor or other control device. The controller 702 is depictedas being operably connected to the pump assembly 710, reservoirswitching valve assembly 770, an external density sensor 750, aninternal density sensor 752, and a telemetry module 780. The controller702 may be used to adjust the pump assembly 710 to, e.g., obtain adesired flow rate, back pressure, etc. In such a capacity, the pumpassembly 710 and controller 702 may operate as a programmable pumpassembly. Although controller 702 is depicted as a separate component,it will be understood that it could be incorporated into one or more ofthe components in the depicted system 700 (e.g., the pump assembly 710,etc.). Also, although pump assembly 710 is depicted as a singlecomponent, it will be understood that pump assembly 710 could includeone, two, three, or more pump mechanisms that may be operatedindependently of each other.

The optional telemetry module 780 may be operatively connected to thecontroller 702 to provide for communication between one or more of thecomponents in system 700 and a user, external programming device, etc.Telemetry control devices, systems and methods that may be used inconnection with the present invention may be described in, e.g., U.S.Pat. No. 5,558,640 (Pfeiler et al.); U.S. Pat. No. 5,820,589 (Torgersonet al.); and U.S. Pat. No. 5,999,857 (Weijand et al.). Althoughtelemetry module 780 is depicted as being connected to the controller702, it will be understood that the telemetry module 780 mayalternatively be connected directly to one or more of the components,e.g., the pump 710, mixing means 713, density sensors 750/752, reservoirswitching valve assembly 770, etc. The telemetry control module 780 mayprovide for one-way or two-way communication.

An optional external density sensor 750 is depicted in connection withFIG. 10 as operably connected to the controller 702 of drug deliverysystem 700. The external density sensor 750 may preferably beimplantable and may be used in a control loop to, e.g., provide densityinformation such that a reservoir from which a drug is to be deliveredcan be selected. If implanted, it may be preferred that the externaldensity sensor 750 be located within the fluid into which the drug ordrugs are to be delivered, e.g., the CSF of a patient.

An optional internal density sensor 752 is also depicted in connectionwith FIG. 10 and may be used to, e.g., sense the density of the drugsolution as delivered to the catheter connection port 712. Such aninternal density sensor 752 may be used in, e.g., a closed loop controlsystem in which, e.g., the density of the CSF of the patient isdetermined and a selected density for the drug solution to be deliveredto the patient is determined. The drug solution can then be formulatedfrom, e.g., the fluids in reservoirs 714 and 715. Before the drugsolution is delivered to the patient, however, its actual density can bemeasured using internal density sensor 752 such that adjustments can bemade (if needed) to provide a drug solution with the desired density.Such a method/system may be described as a closed loop controlsystem/method.

Alternatively, the system may be operated in an open loop configuration.In one embodiment, the external density sensor 750 may be provided todetermine the density of, e.g., the CSF and provide that information tocontroller 702 which can then adjust the density of the drug solutionusing, e.g., reservoir switching valve assembly 770. In such anopen-loop system/method, an internal density sensor 752 may not beprovided, with the density of the drug solution being calculated on,e.g., known or expected values of the different components in reservoirs714 and 715.

In another embodiment of an open-loop control system/method, only aninternal density sensor 752 may be provided such that the actual densityof the drug solution delivered to the catheter connection port 712 canbe measured and adjusted based on a desired density.

Still other embodiments of open-loop control systems and methods may beenvisioned in connection with the present invention.

The system 700 may also preferably include means for mixing 713 if it isdesired to mix the fluids within the reservoirs 714 and 715. The meansfor mixing may take any suitable form and be located in any suitablelocation. For example, the means for mixing 713 may be located withinthe valve assembly 770, pump 710, port 712 or at any other location. Asdiscussed herein, the means for mixing 713 may take a variety of formsincluding both active mixing devices (e.g., mechanical agitators) andpassive mixing devices (e.g., mixing chambers, static mixers, etc.). Themeans for mixing 713 may preferably be connected to the controller 702as shown if control over the means for mixing 713 is desired or requiredduring operation.

Yet another alternative drug delivery system according to the presentinvention is depicted in FIG. 11. In many respects, the system 800 maybe similar to system 700 of FIG. 10. System 800 does, however,preferably include a lumen switching valve assembly 890 located betweenthe catheter 820 and the drug delivery system 800 such that output fromthe system 800 can be directed into the appropriate lumen 826 a and/or826 b of catheter 820. The lumen switching valve assembly 890 and thesystem 800 may preferably be operably connected to, e.g., a controllerlocated within system 800 (as described in connection with, e.g., system700 above). Also, the system 800 may preferably include a pump assemblythat includes two or more independent pump mechanisms to deliver drugsto the different lumens in catheter 820 independently.

In some situations, it may be desired to infuse a drug to multiplelocations that are not collinear such that they cannot be reached by asingle, unbranched catheter. As an example, it may be desired to infusethe same drug into both hemispheres of the brain. To accomplish such amethod, a catheter may be used that includes one or more forks (e.g., a“Y”) at which the catheter splits into two or more separate branches.One example of such an embodiment is depicted in FIG. 12. The catheter920 splits into branches 920 a and 920 b at fork 923.

Branch 922 a includes two infusion sections 927 a and 927 b locatedalong the elongated body of the branch 922 a. As a result, infusionsection 927 b is located between the proximal end 922 of the catheterand the other infusion section 927 a. Although only two infusionsections are shown along branch 920 a, it will be understood that threeor more infusion sections could be provided along the branch 920 a orin-line with each other from the proximal end 922 to the distal end 924a of branch 920 a. In some embodiments, it may be possible that aninfusion section could be located along the length of the catheter 920between the fork 923 and the proximal end 922, with one or more infusionsections located along one or both of the branches 920 a and 920 b.

Also, while catheter 920 includes only one fork and two branches, itshould be understood that catheters of the present invention andsystems/methods using them could include more than one fork and/or thateach fork could include two or more branches.

One or more of the infusion sections on a branched catheter maypreferably include a permeable membrane as described in connection withother embodiments herein. The permeable membranes used in the variousinfusion sections may have the same characteristics or they may bedifferent. For example, the permeable membrane in each infusion sectionmay have the same pore size if it is desired to have an equal amount ofdrug be infused from each infusion section. Sometimes, however, it maybe desired to distribute different amounts of drug to two or more of theinfusion sections. To do so, for example, the pore size of the permeablemembranes in the different infusion sections could potentially beselected to provide the desired relative distribution. For example, alarger pore size could be expected to allow more drug to pass throughthe membrane, while a smaller pore size could be expected to allow lessdrug to pass through the membrane.

The branched catheter 920 could be designed with a single lumen thatsplits at fork 923 to service the infusion sections 927 a and 927 b onbranch 920 a and infusion section 927 c on branch 920 b. Alternatively,however, multiple lumens could be provided to service each of theinfusion sections 927 a, 927 b, and 927 c separately. Such aconfiguration could allow for the delivery of different drug solutionsto the different infusion sections 927 a, 927 b, and 927 c as discussedherein with respect to multiple lumen catheters that are not branched.In still another variation, one infusion section could be serviced by afirst lumen and two or more infusion sections (on the same or differentbranches) could be served by a common lumen (that splits if thecommonly-served infusion sections are located on different branches.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Allpublications mentioned herein are incorporated by reference to discloseand describe the methods and/or materials in connection with which thepublications are cited. Nothing herein is to be construed as anadmission that the present invention is not entitled to antedate suchpublication by virtue of prior invention. Further, the dates ofpublication provided may be different from the actual publication dateswhich may need to be independently confirmed.

As used herein and in the appended claims, the singular forms “a,”“and,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a drug” includes aplurality of drugs and reference to “the lumen” includes reference toone or more lumens and equivalents thereof known to those skilled in theart.

Unless otherwise indicated, all numbers expressing measurements, poresizes, etc. used in the specification and claims are to be understood aspreferably being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the invention are approximations, the numerical values set forth inthe specific examples are reported as precisely as possible. Anynumerical value, however, inherently contain certain errors necessarilyresulting from the standard deviation found in their respective testingmeasurements.

Illustrative embodiments of this invention are discussed and referencehas been made to possible variations within the scope of this invention.These and other variations and modifications in the invention will beapparent to those skilled in the art without departing from the scope ofthe invention, and it should be understood that this invention is notlimited to the illustrative embodiments set forth herein. Accordingly,the invention is to be limited only by the claims provided below andequivalents thereof.

1. A drug delivery system comprising: an implantable pump assembly; twoor more implantable reservoirs operably connected to the implantablepump assembly; a catheter connection port adapted to attach a catheterto the drug delivery system; a reservoir switching valve assemblybetween the two or more implantable reservoirs and the catheterconnection port via the reservoir valve switching assembly, wherein thetwo or more implantable reservoirs can be selectively connected to thecatheter connection port, and wherein two reservoirs of the two or morereservoirs contain fluids having different densities; an implantabledensity sensor configured to sense density of cerebrospinal fluid of apatient in which the sensor is implanted; and a controller operablycoupled to the reservoir switching valve assembly and to the implantabledensity sensor, wherein the controller is configured to cause thereservoir switching valve assembly to alternate between (i) selectivelycoupling one or more of the two or more reservoirs to the catheterconnection port to cause a fluid that is hypobaric relative to thedensity of the cerebrospinal fluid to be delivered to the catheterconnection port, and (ii) selectively coupling a different one or moreof the two or more reservoirs to the catheter connection port to cause afluid that is hyperbaric relative to the density of the cerebrospinalfluid to be delivered to the catheter connection port.
 2. The system ofclaim 1, further comprising a telemetry module operably connected tocontrol the reservoir switching valve assembly.
 3. The system of claim1, further comprising a telemetry module operably connected to thedensity sensor.
 4. The system of claim 1, further comprising means formixing fluids delivered from at least two of the two or more reservoirs,whereby a mixed fluid having a selected density can be obtained based ona density measured by the density sensor.
 5. The system of claim 1,wherein two reservoirs of the two or more reservoirs contain differentdrugs.
 6. The system of claim 5, wherein the different drugs are in drugsolutions having different densities.
 7. The system of claim 1, whereintwo reservoirs of the two or more reservoirs contain the same drug intwo different drug solutions having different densities.
 8. The systemof claim 1, further comprising means for mixing fluids delivered from atleast two of the two or more reservoirs.
 9. The system of claim 8,wherein the means for mixing performs the mixing before the fluids exitthe catheter connection port.
 10. The system of claim 8, furthercomprising a telemetry module operably connected to control the meansfor mixing.
 11. The system of claim 1, further comprising means formodifying flow rate to the catheter connection port.
 12. The system ofclaim 1, wherein the implantable pump assembly comprises at least oneprogrammable pump mechanism.
 13. The system of claim 1, furthercomprising a telemetry module operably connected to control theimplantable pump assembly.
 14. The system of claim 1, wherein theimplantable pump assembly comprises two or more pump mechanisms.
 15. Thesystem of claim 1, further comprising a catheter that comprises aproximal end connected to the catheter connection port, wherein thecatheter comprises a first lumen extending from the proximal end of thecatheter to a first infusion section and a second lumen extending fromthe proximal end of the catheter to a second infusion section.
 16. Thesystem of claim 15, further comprising a lumen switching valve assemblybetween the two or more reservoirs and the catheter, wherein the two ormore reservoirs can be selectively connected to one or both of the firstlumen and the second lumen.
 17. The system of claim 16, furthercomprising a telemetry module operably connected to control the lumenswitching valve assembly.
 18. The system of claim 15, further comprisingmeans for modifying the flow rate through one or both of the first lumenand the second lumen.
 19. The system of claim 15, wherein the two ormore reservoirs comprise a first reservoir connected to the first lumenand a second reservoir connected to the second lumen.
 20. The system ofclaim 19, further comprising a first valve between the first reservoirand the first lumen and a second valve between the second reservoir andthe second lumen.
 21. The system of claim 19, further comprising atelemetry module operably connected to control one or both of the firstvalve and the second valve.
 22. The system of claim 19, furthercomprising means for modifying the flow rate through one or both of thefirst lumen and the second lumen.
 23. A method of delivering one or moredrugs to at least one internal body location using a drug deliverysystem implanted in the body of a patient, wherein the drug deliveryapparatus comprises an implantable pump assembly, two or moreimplantable reservoirs operably connected to the implantable pumpassembly, a catheter connection port adapted to attach a catheter to thedrug delivery system, and a reservoir switching valve assembly betweenthe two or more implantable reservoirs and the catheter connection port,wherein two reservoirs of the two or more reservoirs contain fluidshaving different densities, the method comprising: measuring density ofthe cerebrospinal fluid of a patient using an implanted density sensor;and alternating between (i) selectively connecting one or more of thetwo or more implantable reservoirs to the catheter connection port toobtain a fluid that is hypobaric relative to the measured density of thecerebrospinal fluid; and delivering the hypobaric fluid from the one ormore reservoir of the two or more implantable reservoirs to the catheterconnection port using the implantable pump assembly; (ii) selectivelyconnecting another one or more of the two or more implantable reservoirsto the catheter connection port to obtain a fluid that is hyperbaricrelative to the measured density of the cerebrospinal fluid; anddelivering the hyperbaric fluid from the one or more reservoir of thetwo or more implantable reservoirs to the catheter connection port usingthe implantable pump assembly.
 24. The method of claim 23, furthercomprising controlling the reservoir switching valve assembly from alocation outside of the body of the patient.
 25. The method of claim 23,further comprising receiving a signal from the implanted density sensorindicative of the density of the cerebrospinal fluid as measured. 26.The method of claim 23, further comprising mixing fluids delivered fromat least two of the two or more reservoirs before delivering the drug.27. The method of claim 23, wherein two reservoirs of the two or morereservoirs contain different drugs.
 28. The method of claim 27, whereinthe different drugs are in drug solutions having different densities.29. The method of claim 23, wherein two reservoirs of the two or morereservoirs contain the same drug in two different drug solutions havingdifferent densities.
 30. The method of claim 23, wherein the drugdelivery system further comprises a catheter comprising a proximal endconnected to the catheter connection port, wherein the cathetercomprises a first lumen extending from the proximal end of the catheterto a first infusion section and a second lumen extending from theproximal end of the catheter to a second infusion section, and whereinthe method further comprises passing the drug delivered from the atleast one reservoir of the two or more implantable reservoirs to thecatheter connection port to at least one of the first infusion sectionand the second infusion section.
 31. The method of claim 30, wherein thedrug delivery system comprises a lumen switching valve assembly betweenthe two or more reservoirs and the catheter, wherein the two or morereservoirs can be selectively connected to one or both of the firstlumen and the second lumen.
 32. The method of claim 31, furthercomprising a telemetry module operably connected to control the lumenswitching valve assembly.
 33. The system of claim 1, wherein at leastone of the two reservoirs of the two or more reservoirs contains a drug.34. The system of claim 1, wherein both of the two reservoirs of the twoor more reservoirs contain drugs.
 35. The system of claim 34, whereinboth of the two reservoirs of the two or more reservoirs contain thesame drug.
 36. The method of claim 23, wherein at least one of the tworeservoirs of the two or more reservoirs contains a drug.
 37. The methodof claim 23, wherein both of the two reservoirs of the two or morereservoirs contain drugs.
 38. The method of claim 37, wherein both ofthe two reservoirs of the two or more reservoirs contain the same drug.39. An implantable drug delivery system comprising: an implantable pumpassembly; an implantable density sensor configured to measure density ofcerebrospinal fluid of a patient in which the sensor is implanted; twoor more implantable reservoirs operably connected to the implantablepump assembly, wherein the two or more reservoirs are configured tocontain fluids of differing densities such that (i) selection of fluidsfrom a first of one or more of the two or more reservoirs results in afluid that is hypobaric relative to the density of the cerebrospinalfluid, and (ii) selection of fluids from a second of one or more of thetwo or more reservoirs results in a fluid that is hyperbaric relative tothe density of the cerebrospinal fluid; a catheter connection portadapted to attach a catheter to the drug delivery system; a reservoirswitching valve assembly between the two or more implantable reservoirsand the catheter connection port, wherein the two or more implantablereservoirs can be selectively connected to the catheter connection portsuch that delivery of the hypobaric fluid resulting from selection ofthe first of the one or more reservoirs is configured to alternate withdelivery of the hyperbaric fluid resulting from selection of the secondof the one or more reservoirs.
 40. The system of claim 39, furthercomprising a telemetry module operably connected to control thereservoir switching valve assembly.
 41. The system of claim 39, furthercomprising a telemetry module operably connected to the density sensor.42. The system of claim 39, further comprising means for mixing fluidsdelivered from at least two of the two or more reservoirs, wherein thedensity sensor is operably connected to the means for mixing, whereby amixed fluid having a selected density can be obtained based on a densitymeasured by the density sensor.
 43. The system of claim 39, wherein tworeservoirs of the two or more reservoirs contain different drugs. 44.The system of claim 43, wherein the different drugs are in drugsolutions having different densities.
 45. The system of claim 39,wherein two reservoirs of the two or more reservoirs contain the samedrug in two different drug solutions having different densities.
 46. Thesystem of claim 39, further comprising means for mixing fluids deliveredfrom at least two of the two or more reservoirs.
 47. The system of claim46, wherein the means for mixing performs the mixing before the fluidsexit the catheter connection port.
 48. The system of claim 46, furthercomprising a telemetry module operably connected to control the meansfor mixing.
 49. The system of claim 39, further comprising means formodifying flow rate to the catheter connection port.
 50. The system ofclaim 39, wherein the implantable pump assembly comprises at least oneprogrammable pump mechanism.
 51. The system of claim 39, furthercomprising a telemetry module operably connected to control theimplantable pump assembly.
 52. A method of delivering one or more drugsto at least one internal body location using a drug delivery systemimplanted in the body of a patient, wherein the drug delivery apparatuscomprises an implantable pump assembly, two or more implantablereservoirs operably connected to the implantable pump assembly, acatheter connection port adapted to attach a catheter to the drugdelivery system, and a reservoir switching valve assembly between thetwo or more implantable reservoirs and the catheter connection port, themethod comprising: alternating between: (i) selectively connecting oneor more of the two or more implantable reservoirs to the catheterconnection port to obtain a fluid that is configured to be hypobaricrelative to the density of cerebrospinal fluid, and delivering thehypobaric fluid from the one or more reservoir of the two or moreimplantable reservoirs to the catheter connection port using theimplantable pump assembly; and (ii) selectively connecting another oneor more of the two or more implantable reservoirs to the catheterconnection port to obtain a fluid that is configured to be hyperbaricrelative to the density of the cerebrospinal fluid; and delivering thehyperbaric fluid from the one or more reservoir of the two or moreimplantable reservoirs to the catheter connection port using theimplantable pump assembly.
 53. The method of claim 52, furthercomprising controlling the reservoir switching valve assembly from alocation outside of the body of the patient.
 54. The method of claim 52,further comprising receiving a signal from the implanted density sensorindicative of the density of the cerebrospinal fluid as measured. 55.The method of claim 52, further comprising mixing fluids delivered fromat least two of the two or more reservoirs before delivering the drug.56. The method of claim 52, wherein two reservoirs of the two or morereservoirs contain different drugs.
 57. The method of claim 56, whereinthe different drugs are in drug solutions having different densities.58. The method of claim 52, wherein two reservoirs of the two or morereservoirs contain the same drug in two different drug solutions havingdifferent densities.